Extramitochondrial OPA1 and adrenocortical function

Abstract

We have previously described that silencing of the mitochondrial protein OPA1 enhances mitochondrial Ca(2+) signaling and aldosterone production in H295R adrenocortical cells. Since extramitochondrial OPA1 (emOPA1) was reported to facilitate cAMP-induced lipolysis, we hypothesized that emOPA1, via the enhanced hydrolysis of cholesterol esters, augments aldosterone production in H295R cells. A few OPA1 immunopositive spots were detected in ∼40% of the cells. In cell fractionation studies OPA1/COX IV (mitochondrial marker) ratio in the post-mitochondrial fractions was an order of magnitude higher than that in the mitochondrial fraction. The ratio of long to short OPA1 isoforms was lower in post-mitochondrial than in mitochondrial fractions. Knockdown of OPA1 failed to reduce db-cAMP-induced phosphorylation of hormone-sensitive lipase (HSL), Ca(2+) signaling and aldosterone secretion. In conclusion, OPA1 could be detected in the post-mitochondrial fractions, nevertheless, OPA1 did not interfere with the cAMP - PKA - HSL mediated activation of aldosterone secretion.

Keywords: (mitochondrial) Translocation Protein (previously peripheral benzodiazepine receptor); A-kinase anchoring protein; AKAP; Aldosterone; COX IV; Ca(2+)/calmodulin-dependent kinase II; CaMKII; H295R cell; HSL; Hormone sensitive lipase; IMM; IMS; Mfn 1; Mitochondria; OMM; OPA1; Optic Atrophy 1; PDI; PKA; Plin; StAR; Steroidogenic Acute Regulating Protein; TSPO; [Ca(2+)](m); cytochrome c oxidase IV; db-cAMP; dibutiryl-cAMP; emOPA1; extramitochondrial OPA1; hormone-sensitive lipase; inner mitochondrial membrane; mitochondrial Ca(2+) concentration; mitochondrial intermembrane space; mitofusin 1; outer mitochondrial membrane; perilipin; protein disulfide isomerase; protein kinase A.